Systems and methods for detecting leaks in an electromagnetic flowmeter

ABSTRACT

An electromagnetic flowmeter has a flowtube configured to carry a conductive fluid. The flowtube has wall made of a conductive material. The wall has an inner surface surrounding a fluid flow path for the fluid. A non-conductive liner is positioned to electrically insulate the flowtube wall from the fluid. The flowtube and non-conductive liner define an electrode mounting hole. An electrode extends through the electrode mounting hole. The electrode and the non-conductive liner form a fluidic seal between the electrode mounting hole and the fluid flow path. At least a portion of the electrode is arranged in fluid communication with the flowtube within the electrode mounting hole. A short circuit detector can detect failure of the seal when conductive fluid that has leaked past the seal creates a short circuit as a result of the fluid communication between the flowtube and the electrode mounting hole.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/659,210, filed Mar. 16, 2015, the entire contents of whichare hereby expressly incorporated by reference, including the contentsand teachings of any references contained therein.

FIELD OF INVENTION

Aspects of the present invention relate generally to electromagneticflowmeters and more particularly to systems and methods for detectingleakage of fluid from a flowtube of an electromagnetic flowmeter.

BACKGROUND

Electromagnetic flowmeters (which are sometimes referred to as magneticflowmeters or “mag meters”) measure the flow rate of an electricallyconductive fluid through a flowtube. In a conventional electromagneticflowmeter, electrical coils are mounted on opposite sides of the tubeand energized to produce an electromagnetic field perpendicular to thedirection of fluid flow in the flowtube. When a conductive fluid flowsthrough the electromagnetic field, an electric field is generated in thefluid that can be measured to determine the flow rate. In a typical setup, a pair of electrodes extends through the wall of the flowtube andinto the fluid for measuring the strength of the electric field todetermine the flow rate. Sometimes additional electrodes extend throughthe wall of the flowtube into a conduit therein in order to provideempty pipe detection or to ground the liquid. Each point where anelectrode extends through the flowtube wall into the conduit requires aso-called process penetration. As illustrated in FIG. 1, a conventionalelectrode 15 includes a head 19 and a shank 21 extending away from thehead. The shank 21 is inserted into an opening 17 forming the processpenetration so the head 19 is in the conduit 7 formed by the flowtube 3and so the shank extends through the flowtube wall 5. A fastener 25(e.g., a threaded nut) is used to hold the electrode is in thisposition.

The process penetrations should be sealed to keep the fluid from leakinginto the process penetration as it flows through the flowmeter 1. Oneway this is done is to provide serrations 23 on the back side of thehead 19 of each electrode 15. The inner surface of the flow tube 3 iscommonly lined with an electrically insulating and chemically resistantliner 11 to prevent the conductive fluid from creating a short circuitbetween the electrode 15 and the flowtube wall 5, which is commonly madeof an electrically conductive material such as metal. Thus, when the nutor other fastener 25 is tightened, the serrations 23 on the back of theelectrode head 19 dig into the liner 11 and form a seal between the headof the electrode 15 and the liner. This seal is known as the primaryseal. The shank 21 of the electrode 15 is insulated from theelectrically conductive part of the flowtube wall 5 by an insulatingsheath 31 surrounding at least the segment of the shank that is adjacentthe conductive flowtube wall. If fluid leaks past the primary seal, itwill also have to flow past the insulating sheath 31 to completelyescape through the process penetration. As a result, fluid can leakthrough the liner 11 and contact the flowtube 3 without any evidence ofthe leak being visible from outside the flowtube 3.

The fluids metered by electromagnetic flowmeters can include verycorrosive and/or caustic materials. In some processes the fluids canalso be at a fairly high temperature when they flow through theelectromagnetic meter, which can increase the rate at which the fluidcauses damage to other materials (e.g., the flowtube wall 5). Thepresent inventors have noted that fluids may leak past the primary sealand cause extensive corrosion of the flowtube wall 5 before a leak isdetected. This can present a significant hazard because damage to theflowtube wall 5 can impair the pressure containment capability of theflowtube. Thus, the leak may not be detected until the flowtube burstsand releases the corrosive fluid in a catastrophic failure.

SUMMARY

One aspect of the invention is an electromagnetic flowmeter. Theflowmeter has a flowtube configured to carry a flowing conductive fluid.The flowtube has a flowtube wall including a conductive material. Theflowtube wall has an inner surface surrounding a fluid flow path for theconductive fluid. A non-conductive liner is positioned to electricallyinsulate the flowtube wall from the conductive fluid. The flowtube andnon-conductive liner define an electrode mounting hole. An electrodeextends through the electrode mounting hole. The electrode and thenon-conductive liner form a fluidic seal between the electrode mountinghole and the fluid flow path. At least a portion of the electrode isarranged in fluid communication with the flowtube within the electrodemounting hole.

Another aspect of the invention is a method of making an electromagneticflowmeter. The method includes providing a flowtube including an axisalong which fluid can flow through the flowtube. The flowtube also hasan outer surface and an inner surface. The flowtube is electricallyconductive and configured so that the inner surface is electricallyinsulated from fluid flow passing through the flowtube. The flowtubeincludes an electrode mounting hole extending radially with respect tothe axis through a wall of the flowtube, including the outer surface andthe inner surface. An electrode is installed in the electrode mountinghole so that at least a portion of the electrode in the mounting hole isin fluid communication with the flowtube wall within the electrodemounting hole. The electrode is operatively sealed with the outer andinner surfaces of the flowtube. A short circuit detector is connected tothe flowtube and electrode, whereby should the seal between theelectrode and the inner surface of the flowtube fail, fluid flowingthrough the flowtube and entering the electrode mounting hole has accessto the electrode for creating a short circuit detectable by the shortcircuit detector.

Yet another aspect of the invention is a leak detection system fordetecting a leak in an electromagnetic flowmeter having anelectromagnetic field source for generating an electromagnetic field ina fluid flowing through the flowmeter that changes periodically at adrive frequency and first and second electrodes to detect a voltageinduced in the fluid. The leak detection system includes a leakdetection processor connected to the first and second electrodes toreceive first and second signals representative of the voltage detectedby the first and second electrodes, respectively. The leak detectionprocessor is configured to analyze a content of at least the firstsignal at the drive frequency to determine whether the first signal isaffected by a leak in the flowmeter and provide an output indicative ofa detected leak when the leak detection processor determines that thefirst signal is affected by the leak in the flowmeter.

Still another aspect of the invention is a method for detecting a leakin an electromagnetic flowmeter having an electromagnetic field sourceconfigured to generate an electromagnetic field in a fluid flowingthrough the flowmeter that changes periodically at a drive frequency andat least first and second electrodes configured to detect a voltageinduced in the fluid in response to the electromagnetic field. Themethod includes analyzing a content of a signal from at least one of thefirst and second electrodes at the drive frequency. A leak in theflowmeter is detected using the content of the first signal. Anindication of a detected leak is provided when the leak is detected.

Other objects and features of the invention will be in a part apparentand in part pointed out hereinafter.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side elevation of a prior art electromagnetic flowmeterillustrated in cross section showing structures associated with aprocess penetration for an electrode;

FIG. 2 is a side elevation of one embodiment of an electromagneticflowmeter of the present invention illustrated in cross section showingstructures associated with a process penetration for an electrode;

FIG. 3 is a schematic diagram illustrating one embodiment of a circuitfor early leak detection at the process penetration illustrated in FIG.2;

FIG. 4 is a diagram similar to FIG. 2 showing schematically a measuredresistance when no leak is detected;

FIG. 5 is a diagram similar to FIG. 4 showing schematically anothermeasured resistance when a leak is detected;

FIG. 6 is a side elevation of another electromagnetic flowmeter of thepresent invention illustrated in cross section showing structuresassociated with two process penetrations for electrodes;

FIG. 7 is a diagram comparing induced voltages detected at respectiveelectrodes of the flowmeter and the summation thereof during normaloperating conditions to the corresponding voltages in case of a leak;

FIG. 8 a schematic diagram illustrating an example of a circuit for leakdetection;

FIG. 9 is a flowchart illustrating the steps and decision block of onemethod of detecting a leak in the flowmeter of FIG. 6 using the circuitof FIG. 8;

FIG. 10 is a schematic diagram illustrating another circuit for leakdetection in the flowmeter of FIG. 6; and

FIG. 11 is a flowchart illustrating the steps of another method ofdetecting a leak in the flowmeter of FIG. 6 using the circuit of FIG.10.

Corresponding reference characters represent corresponding featuresthroughout the drawings.

DETAILED DESCRIPTION

Referring now to the drawings, first to FIG. 2, one embodiment of anelectromagnetic flowmeter is generally designated 101. The flowmeter 101includes a flowtube 103 configured to carry a flowing conductive fluidthrough the flowmeter 101. For example, the flowtube 103 suitablyincludes a generally cylindrical or tubular wall 105 having an innersurface surrounding a flow path 107 extending between opposite ends ofthe flowtube for flow of fluid through the flowmeter 101. The flowtube103 is suitably made of an electrically conductive material, such asstainless steel or another suitable metal. A non-conductive liner 111lines the inner surface of the flowtube wall 105 to electricallyinsulate the flowtube wall from the conductive fluid. The non-conductiveliner 111 may have any of several suitable configurations, such as acoating, a separate liner attached to the inner surface of the flowtube103, a treatment of the material of the flowtube adjacent the innersurface to provide a few examples.

The flowmeter 101 has an electrode 115 extending through a processpenetration formed by an electrode mounting hole 117 extending throughthe flowtube wall 105 and the non-conductive liner 111. The electrode115 includes a head 119 and a shank 121 extending away from the head.The shank 121 has a shank diameter D1 and the head 119 has a headdiameter D2 larger than the shank diameter. As illustrated in FIG. 2,the shank 121 extends through the electrode mounting hole 117 in theflowtube wall 105 and non-conductive liner 111. Though not illustratedfor clarity, the shank 121 is suitably threaded. The end of the shank121 opposite the head 119 extends through the flowtube 103 to anexterior of the flowtube. A fastener 125 holds the electrode 115 so thehead 119 of the electrode is in contact with the liner 111. The fasteneris suitably a threaded nut 125 on the threaded shank 121. The fastener125 is capable of applying tension to the shank 121 to draw the head 119of the electrode 115 tightly against the liner 111. In the illustratedembodiment, for example, the threaded nut 125 can be tightened against anon-conductive washer 133 adjacent the exterior of the flowtube 103 topull the shank 121 farther out of the electrode mounting hole 117 anddraw the head 119 tightly against the liner 111 to form a seal. Thenon-conductive washer 133 suitably prevents the fastener 125 fromcreating an unwanted electrical connection between the flowtube 103 andthe electrode shank 121. The head 119 suitably has a plurality ofserrations or teeth 123 positioned to contact the liner 111 when thefastener 125 is tightened. However, the serrations can be omitted withinthe scope of the invention. Also, although in the illustrated embodimentthe electrode 115 includes a threaded shank 121 and the fastenerincludes a threaded nut 125, it is understood that other types offastening devices may be used without departing from the scope of theinvention.

The electrode shank 121 extends through the conductive flowtube wall 105and is everywhere spaced apart from the flowtube wall. In theillustrated embodiment, a non-conductive spacer 131 is disposed aroundat least a portion of the shank 121 in the electrode mounting hole 117between the shank and the flowtube wall 105. The illustrated spacer 131has at least one fluidic path 135 extending between the electrode shank121 and the flowtube wall 105. Under normal circumstances, the fluidicpath 135 defined by the spacer 131 is substantially devoid of fluid orother conductive materials. For example, the fluidic path 135 cansuitably be filled with air or another non-conductive gas. The spacer131 is positioned to insulate the electrode 115, and in particular theshank 121 of the electrode, from the conductive flowtube wall 105 at theprocess penetration under normal circumstances. However, in the eventfluid flowing through the flowmeter 101 leaks through the primary sealformed between the head 119 of the electrode 115 and the non-conductiveliner 111 and into the fluidic path 135, the conductive fluid canestablish a low-resistance electrical connection between the electrode115 and the conductive flowtube wall 105. Leaking fluid in the fluidicpath 135 establishes a short circuit between the electrode 115 andground (i.e., the flowtube 103) that can be detected without any visualevidence of the leak.

In the illustrated embodiment, the spacer 131 is a cylindrically-shapedsleeve positioned so the electrode shank 121 extends through an axialhole in the sleeve for receiving the shank. In this embodiment, thefluidic path 135 includes a transverse hole extending laterally throughthe cylindrically-shaped sleeve 131. In particular, the hole 135 extendslaterally through the sleeve 131 from the shank 121 to the flowtube wall105. Though the illustrated embodiment uses the spacer 131, it is alsocontemplated that the electrode shank 121 may be secured in spaced apartrelationship with the flowtube wall 105 (and be electrically insulatedtherefrom) other ways without departing from the scope of the invention.For example, in some embodiments (not shown), a fastener secures theelectrode to the wall in a position in which the shank extends through aprocess penetration but does not make electrical contact with the wall.Likewise, various differently sized and shaped spacers can be usedwithin the broad scope of the invention. In these alternativeembodiments, the flowmeter includes a fluidic path between an electrode(specifically, in some embodiments, an electrode shank) and a conductiveflowtube wall. The fluidic path is configured so that, in the eventconductive fluid leaks into the fluidic path, the conductive fluid thatleaks into the fluidic path establishes an electrical connection betweenthe electrode and the conductive flowtube wall. Likewise, in theseembodiments the electrode is electrically insulated from the conductiveflowtube wall as long as the conductive fluid does not leak into thefluidic path. In certain of these embodiments, at least a portion of theelectrode (e.g., a portion of the shank) and a portion of the flowtubein the electrode mounting hole are in opposed relation, free ofobstruction therebetween.

Referring again to the embodiment of FIG. 2, the flowmeter 101 includesa system 141 that monitors for the presence of fluid in the fluid path135 by assessing electrical impedance between the electrode 115 and theconductive flowtube wall 105. For example, the flowmeter 101 suitablyincludes a short circuit detector 141 configured to detect whether ornot conductive fluid is in the fluid path 135. A suitable short circuitdetector can be formed by any electrical components that can beconfigured to detect electric current passing through the fluidic path135 between the electrode shank 121 and the flowtube wall 105. Somewhatrelatedly, a suitable short circuit detector can be formed by anyelectrical components that can be configured to detect a change in theoverall electrical resistance in the electrical paths between theelectrode 115 and the flowtube wall 105. The electrical resistance inthe fluidic path 135 will be relatively high when the fluidic path issubstantially devoid of fluid and much lower if the fluidic path isfilled with conductive fluid. Those skilled in the art will be familiarwith many different ways to detect the formation of a short circuitbetween two nodes in an electrical system (e.g., the electrode and theflowtube wall).

Referring to FIGS. 3-5, in a suitable embodiment the monitoring system141 includes a comparator 143 that compares the resistance between twonodes (the flowtube 103 and the electrode 115) to a reference value. Asdiscussed above, the flowtube 103 is made from conductive material, andthe fluid flowing through the flowtube is likewise conductive. Thenon-conductive liner 111 extends only a certain length L1 (FIG. 4) fromthe electrode 115. The fluid in the flow path 107, in normal,non-leaking conditions, electrically connects the electrode 115 to theflowtube 103 at the location where the non-conductive liner 111 ends.Thus, current passes between the electrode 115 and the flowtube 103 overa relatively long length L1 of fluid around the upstream and downstreamends of the liner 111 under normal, non-leaking conditions. For purposesof explanation, the illustrated liner 111 does not coat the entire innersurface of the flowtube 103. However, it should be understood that, insome embodiments, a non-conductive liner will coat the full length ofthe flowtube. In certain of these embodiments, the flowmeter is fluidlyconnected to an electrically conductive pipeline. Fluid between theelectrode head and the conductive pipeline will provide a normalconnection between the electrode and ground. When the electricalresistance in the path 135 is relatively high (no leaks), the resistancebetween the electrode 115 and the flowtube wall 105 is approximately thesame as the resistance to flow of this current through the conductiveliquid. Still other connections between an electrode and ground mayestablish the normal electrical resistance between an electrode and acorresponding flowtube wall (ground) without departing from the scope ofthe invention. One skilled in the art will appreciate that techniquesdescribed with respect to the illustrated embodiment for detecting adeviation in the normal impedance between the electrode 115 and theflowtube 103 can be readily adapted to other normal connections betweenan electrode and ground.

As shown best in FIG. 4, when no fluid leaks past the non-conductiveliner 111, the resistance between the electrode 115 and the flowtube 103is substantially equal to the normal resistance R_(F), a relatively highvalue, which is directly related to the length L1 of fluid connectingthe conductive flowtube 103 to the electrode 115 as well as the fluid'sresistivity. However, as shown in FIG. 5, when fluid leaks past thenon-conductive liner 111, a new, parallel current path is created in thefluidic path 135. The length L2 of the fluidic path 135 is much shorterthan the length L1 of fluid between the electrode head 119 and the endof the flowtube liner 111. Thus, the short circuit electrical resistanceR_(L) between the flowtube 103 and the electrode 115 along the fluidpath 135, is much lower than the normal resistance R_(F). When fluidleaks past the non-conductive liner 111, the total resistance R_(T)between the flowtube 103 and the electrode 115 is equal to the combinedresistances of R_(F) and R_(L) in parallel:

$R_{T} = {\frac{R_{F}*R_{L}}{R_{F} + R_{L}}.}$

When fluid leaks past the non-conductive liner 111 and into the fluidicpath 135, the total resistance R_(T) between the flowtube 103 and theelectrode 115 is much lower than when there is no leak. The normal(e.g., when there is no leak) resistance R_(F) between the flowtube 103and the electrode 115 can be calculated based on the type of fluidflowing through the flow path 107 (e.g., the resistivity of the fluid)and the length L1 between the electrode head 119 and the end of thenon-conductive liner 111. Referring again to FIG. 3, the short circuitdetector 141 is configured to detect the presence of conductive fluid inthe fluidic path 135. An adjustable reference generator 145 supplies areference resistance value R_(ref) to the comparator 145. Suitably, thereference resistance value R_(ref) is set at a value slightly lower thanthe expected fluid resistance R_(F) (e.g., between about 80% and about95% of the expected fluid resistance R_(F)) and higher than the expectedtotal resistance R_(T) in the event of a short circuit. The resistancebetween the flowtube 105 and the electrode 115 is measured, and themeasured resistance R_(meas) is supplied to another input of thecomparator 143. There are various ways the resistance can be measured.For example, a known amount of current can be driven between theflowtube 105 and the electrode 115 for a brief time and the inducedvoltage during this time can be used as a measure of the resistanceand/or used to calculate the resistance. The resistance can be measuredin other ways without departing from the scope of the invention. Thecomparator 143 receives the measured resistance and compares it with thereference value R_(ref). If the measured resistance R_(meas) is lessthan the reference value R_(ref), the short circuit detector 141 isconfigured to output an alarm. For example, it may output a signal thatcauses a local display to indicate the detection of a leak. Likewise, itmay output a signal that is transmitted to a distributed control system.

Although only one electrode is illustrated in FIGS. 2, 3, and 5, it isunderstood that the flowmeter will generally have at least twoelectrodes on opposite sides of the flowtube. It is also understood thatmore than two electrodes can be included in the flowmeter, such as toprovide empty pipe detection or to ground the fluid flowing through themeter.

Referring to FIG. 6, another embodiment of an electromagnetic flowmeterconfigured to detect a fluid leak is generally indicated at referencenumber 201. The electromagnetic flowmeter 201 includes a conductiveflowtube 203 and a non-conductive inner liner 211 that insulates theflowtube from a conductive fluid flowing in a flow path 207 extendingaxially through the flowtube. First and second electrodes 215A, 215Bextend through respective process penetrations 217 in the wall 205 ofthe flowtube 203 at diametrically opposed positions. A pair of drivecoils (broadly, an electromagnetic field source; not shown) are locatedadjacent the outside of the flowtube 203 at diametrically opposedpositions angularly spaced from the positions of the electrodes 215A,215B about a longitudinal axis of the flowtube 203. The drive coilsgenerate an electromagnetic field in the conductive fluid flowingthrough the flowtube 203, and the electrodes 215A, 215B detect a voltageinduced in the fluid as the fluid flows through the electromagneticfield. Suitably, the drive coils generate an electromagnetic field thathas an electromagnetic field direction, and the electrodes 215A, 215Bdetect respective voltages induced in the fluid at diametrically opposedpositions oriented perpendicular to the electromagnetic field direction.

In the illustrated embodiment, an insulating sheath 231 separates theshank 221 of each of the first and second electrodes 215A, 215B from theflowtube wall 205, and a non-conductive washer 233 provides electricalinsulation between the flowtube wall 205 and the fastener 225 thatsecures each electrode to the flowtube wall. Thus, as in the previousembodiment, under normal operating conditions, each electrode 215A, 215Bis electrically insulated from the flowtube wall 205 at the processpenetration 217. When fluid leaks past the seal formed between the head219 of either electrode 215A, 215B and the inner liner 211, it createsan electrical connection between the respective electrode and theflowtube wall 205 that is not present under normal operating conditions.Though the illustrated insulating sheath 231 provides a transverse hole235 for creating a direct fluid path between the flowtube wall 205 andthe respective electrode 215A, 215B, it will be understood that, even inthe absence of such a sheath, leaking fluid can penetrate the seamsbetween the insulating and conductive components to create an undesiredelectrical connection between the electrode and flowtube wall. A leakdetection system 241 detects when a leak in the flowtube creates anundesired electrical connection between one of the first and secondelectrodes 215A, 215B and the inner liner 211.

Referring to FIG. 7, the drive coils are configured to generate anelectromagnetic field 251 that changes periodically at a drive frequencyf. The drive frequency can be constant or variable. In the illustratedembodiment, the electromagnetic field 251 is reversed at a constantdrive frequency f. However, other changes in the electromagnetic field251 can also be made periodically without departing from the scope ofthe invention. The first electrode 215A produces a first voltage signal253A representative of an induced voltage in the fluid at the head 219of the first electrode. Likewise, the second electrode 215B produces asecond voltage signal 253B representative of an induced voltage in thefluid at the head 219 of the second electrode. Respective flow-inducedportions of the first and second voltage signals 253A, 253B accuratelyrepresent the induced voltages and are related to the flow rate of thefluid in the flowtube 203. However, respective noise portions of thevoltage signals 253A, 253B are attributable to sources of noise (e.g., aDC potential between the first and second electrodes 215A, 215B) anddetract from the accuracy of the voltage signals. One skilled in the artwill appreciate that the flow rate of the fluid flowing through the flowpath 207 is related to the difference between the flow-induced portionsof the first and second voltage signals 253A, 253B under normaloperating conditions.

Under normal operating conditions each of the first and second voltagesignal 253A, 253B changes periodically with the periodic changes inelectromagnetic field strength (i.e., at the drive frequency f). Theflow-induced portion of the first voltage signal 253A is equal inmagnitude and opposite in sign (i.e., 180° out of phase) with respect tothe flow-induced portion of the second voltage signal 253B under normaloperating conditions. However, if the flowmeter 201 has a fluid leak, ashort circuit can be created between either of the first and secondelectrodes 215A, 215B and the flowtube sidewall 205. For example, when afluid path forms between one the second electrode 215B and the flowtubewall 205, the fluid path electrically connects the electrode and theflowtube wall 205, creating a short circuit at the electrode. As aresult, the second voltage signal 253B produced by the second electrode215B is substantially constant (i.e., does not vary significantly inresponse to variations in the electromagnetic field induced in the fluidby periodic changes in the drive signal 251), as illustrated in FIG. 7.

Referring to FIGS. 7 and 8, the leak detection system 241 is operativelyconnected to the first and second electrodes 215A, 215B to receive thefirst and second voltage signals 253A, 253B produced by the electrodes.The leak detection system 241 is configured to analyze a content of theat least one of the voltage signals 253A, 253B at the drive frequency fto determine whether the signal is affected by a leak. For example, theleak detection system 214 can use the drive frequency content of one orboth of the signals 253A, 253B to determine whether either or both ofthe signals vary periodically at the drive frequency for whether theamount of variation in either of the signals at the drive frequency issuppressed below a normal (i.e., significant) amount of variation. Whenthe leak detection system 241 determines that one or more of the signalsproduced by the electrodes 241 are affected by a leak in the flowmeter,it provides an output indicative of a detected leak.

The leak detection system 241 illustrated in FIG. 8 includes a summingamplifier 261 operatively connected to the first and second electrodes215A, 215B to receive the first and second voltage signals 253A, 253B.The summing amplifier 261 is configured to add the voltage signals 253A,253B to generate a summation signal. As discussed in further detailbelow, the leak detection system 241 analyzes a content of the summationsignal at the drive frequency to determine whether either of the firstand second voltage signals 253A, 253B is affected by a leak. A primarysource of noise in the summation signal is caused by an inherent DCpotential between the first and second electrodes 215A, 215B. The DCpotential can be a differential mode potential, a common mode potential,or combination differential and common mode potential. Under normaloperating conditions, the flow-induced portion of the first voltagesignal 253A is equal in magnitude and opposite in sign (i.e., 180° outof phase) with respect to the second voltage signal 253B. Thus when nonoise is present, the output of the summing amplifier 261 should be asubstantially constant zero signal. However, the inherent DC potentialand other noise can cause the sum of the first and second electrodesignals 253A, 253B under normal operating conditions to be non-zero. Tomitigate the effects of the DC potential between the two electrodes, ahigh pass filter 263 with a cutoff frequency set lower than the drivefrequency receives the output of the summing amplifier 261. The highpass filter 263 suppresses at least a portion of the summation signalattributable to the DC potential between the first and second electrodes215A, 215B.

With further reference to FIGS. 7 and 8, under normal operatingconditions the high pass filter 263 outputs a filtered summation signal265 that is substantially constant and substantially close to zero.However, when, for example, fluid leaks through the seal formed betweenthe head 219 of the second electrode 215B and the liner 211, a shortcircuit is created. As illustrated in FIG. 7, when a short circuit isformed between the second electrode 215B and the flowtube wall 205, thesecond voltage signal 253B becomes substantially constant. As a result,the second voltage signal 253B is not equal in magnitude and opposite insign with respect to the first voltage signal 253A, and the summationsignal 265 becomes periodic in nature. Accordingly, the leak detectionsystem 241 can determine whether either of the first and second voltagesignals 253A, 253B is affected by a leak in the flowmeter 201 bydetecting the presence of significant periodic changes in the summationsignal 265.

The leak detection system 241 in FIG. 8 includes an analog-to-digitalconverter 271 that samples the summation signal 265 and generates adigital output signal (i.e., a digital summation signal) representativeof the summation signal. A digital leak detection processor 273 receivesthe digital summation signal and analyzes a content of the summationsignal 265 at the drive frequency f to determine whether either of thevoltage signals 253A, 253B is affected by a leak in the flowmeter.Though the high pass filter 263 can eliminate some of the DC offset fromthe output of the summing amplifier 261 (including both common anddifferential DC offset), a portion of the summation signal 265 can stillbe attributable to the DC potential between the first and secondelectrodes 215A, 215B. Moreover, the energy content of the summationsignal 265 still includes frequencies above the cutoff frequency of thehigh pass filter 263.

To minimize the effect of this noise on the leak determination, the leakdetection processor 273 performs a Fourier analysis (e.g., a digitalFourier transform) on the summation signal 265 to analyze the energycontent of the summation signal 265 at the drive frequency f. In asuitable embodiment, the leak detection processor 273 uses a Fouriertransform to calculate a spectral number F(bin) for the summation signal265 at the drive frequency f and converts the spectral number into anamplitude V_(f) of the summation signal at the drive frequency (i.e., arepresentation of the energy of the summation signal at the drivefrequency). Under normal operating conditions, the drive frequencyamplitude V_(f) should be close to zero. When the leak detectionprocessor determines the amplitude V_(f) has strayed too far from zero(e.g., by comparing the amplitude to a threshold), it determines thatone of the first and second voltage signals 253A, 253B is affected by aleak in the flowmeter 201 and provides an output indicative of adetected leak.

Referring to FIG. 9, in one method 301 of detecting a leak in theflowmeter 201, the analog-to-digital converter 271 samples the summationsignal 265 (step 311) during a sampling interval corresponding in timewith one or more complete cycles of the drive signal 251 (i.e., anintegral number of drive cycles). At step 313 the leak detectionprocessor 273 stores N samples of the summation signal 265 taken duringthe sampling interval in a buffer. Thus, the buffer stores a digitalrepresentation of the summation signal 265 over one or more completedrive cycles. For example, in one embodiment, the drive frequency f is aconstant low frequency (e.g., 7 Hz) and the analog-to-digital converter271 samples the summation signal 265 at a high frequency (e.g., 4800Hz). The buffer preferably stores a large number of samples (e.g., 3500samples), which represents several complete drive cycles (e.g., 5 drivecycles).

At step 315, the leak detection processor 273 uses Fourier analysis(e.g., the discrete Fourier transform) and the N samples stored in thebuffer to calculate a spectral number F(bin) for the summation signal265 at the drive frequency f. For example, the leak detection processor273 can use the discrete Fourier transform to calculate a frequencyspectrum for the summation signal 265 and determine the spectral numberF(bin) from the frequency spectrum, where bin corresponds with thespectral array index for the drive frequency f. The bin index for thedrive frequency f can, in a suitable embodiment, be calculated bydividing the sampling frequency by the number of samples N, plus 1. Asan alternative to calculating a frequency spectrum, the leak detectionprocessor 273 can use Fourier analysis to calculate the drive frequencyspectral number F(bin) directly using techniques such ascross-correlation or autocorrelation. At step 317 the leak detectionprocessor 273 determines the amplitude V_(f) of the summation signal 265at the drive frequency f using equation 1.

$\begin{matrix}{V_{f} = {{F({bin})}{\frac{\pi}{N}.}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

The amplitude V_(f) is representative of the energy in the summationsignal 265 at the drive frequency f. The number of samples N suitablycorresponds with an integral number of drive cycles. If the number ofsamples N does not corresponds to an integral number of drive cycles,the drive frequency will fall between two points in the frequencydomain. The calculation would be less accurate due to spectral leakage.However, a gross measurement can be sufficient to detect a leak. Thus,it is understood the number of samples N does not need to be limited tothe number of samples in an integral number of drive cycles to practicethe invention.

At step 319 the leak detection processor 273 receives a differencesignal V_(Δ) representative of magnitude of a difference between thefirst and second voltage signals 253A, 253B from a flow rate measurementsystem (not shown) of the flowmeter 201. The leak detection processor273 dynamically determines a threshold P as a percentage (e.g., fromabout 10 percent to about 40 percent) of the voltage difference V_(Δ) atstep 321. At decision block 323, the leak detection processor 273compares the threshold P to the amplitude V_(f) of the summation signal265 at the drive frequency f. If the amplitude V_(f) is greater than thethreshold P, the leak detection processor 273 provides an indicationthat one of the first and second voltage signals 253A, 253B is affectedby a leak in the flowmeter 201 (step 325). If the amplitude V_(f) is notgreater than the threshold P, the leak detection method 301 restarts atstep 311. Though the illustrated embodiment dynamically calculates thethreshold P as a percentage of the voltage difference V_(Δ), it will beunderstood that other embodiments can compare the amplitude V_(f) of thesummation signal 265 at the drive frequency f to a constant threshold todetermine whether a leak in the flowmeter 201 affects either of thevoltage signals 253A, 253B.

Referring to FIG. 10, another embodiment of a leak detection systemsuitable for use with the flowmeter 201 is generally indicated atreference number 441. The leak detection system 441 includes amultiplexer 461 that is operatively connected to the first and secondelectrodes 215A, 215B to receive the first and second voltage signals253A, 253B from the electrodes. The multiplexer 461 is configured togenerate a multiplexed signal, which includes alternating sequences ofthe voltage signals 253A, 253B spliced together serially in the timedomain. A high pass filter 463 receives the multiplexed signal from themultiplexer 461 and suppresses a portion of the multiplexed signalattributable to a DC potential between each of the first and secondelectrodes 215A, 215B and ground. An analog-to-digital converter 471samples the output of the high pass filter 463 and generates a digitaloutput representative of the filtered multiplexed signal. As discussedin further detail below, a leak detection processor 473 receives thedigital filtered multiplexed signal and uses it to analyze a content ofthe first voltage signal 253A at the drive frequency f and a content ofthe second voltage signal 253B at the drive frequency. The leakdetection processor 473 compares the drive frequency contents of thefirst and second voltage signals 253A, 253B to determine whether eitherof the first and second voltage signals is affected by a leak. Thoughthe illustrated leak detection processor 473 receives the first andsecond voltage signals 253A, 253B from a single input using amultiplexed signal, it is also contemplated that another leak detectionprocessor could perform a similar processor by receiving the first andsecond voltage signals on two separate inputs.

Referring to FIG. 11, in one method 501 of detecting a leak in theflowmeter 201 using the leak detection system 441, the analog-to-digitalconverter 471 samples the digital multiplexed signal during first andsecond sampling intervals (steps 511, 513). Suitably, the samples fromthe first sampling interval define a first sample set representing thefirst voltage signal 253A and corresponding in time with one or morecomplete drive cycles (step 511). Likewise the samples from the secondsampling interval suitably define a second sample set representing thesecond voltage signal 253B and corresponding in time with one or morecomplete drive cycles (step 513). The leak detection processor 473stores N_(A) samples from the first sample set in a first buffer (step515), which collectively form a digital representation of the firstvoltage signal 253A during the first sampling interval. The leakdetection processor 473 likewise stores N_(B) samples from the secondsample set in a second buffer (step 517), which collectively form adigital representation of the second voltage signal 253B during thesecond sampling interval.

To minimize the effect of noise on the leak determination, the leakdetection processor 473 uses Fourier analysis to calculate a frequencyspectrum for each of the first and second voltage signals 253A, 253Bfrom the first and second sample sets stored in the first and secondbuffers (steps 519, 521). Additionally or in the alternative, the leakdetection processor 473 calculates a spectral number F(bin)_(A),F(bin)_(B) for each of the first and second voltage signals 253A, 253Bfrom the stored first and second sample sets. Using equation 1 and thespectral numbers F(bin)_(A) and F(bin)_(B), the leak detection processor473 calculates respective amplitudes V_(f,A), V_(f,B) of the first andsecond voltage signals 253A, 253B at the drive frequency f (steps 523,525).

As discussed above, under normal operating conditions, the flow-inducedportions of the first and second voltage signals 253A, 253B will besubstantially equal in magnitude. Thus, one skilled in the art willappreciate that the amplitudes V_(f,A), V_(f,B) of the first and secondvoltage signals 253A, 253B, which represent the amount of energy in therespective signals at the drive frequency f, will be substantially equalunder normal operating conditions. However, when a leak creates a shortcircuit at, for example, the electrode 215B as shown in FIG. 7, theamplitude V_(f,B) of the voltage signal 253B at the drive frequency fwill be significantly lower than the amplitude value V_(f,A) of thevoltage signal 253A at the drive frequency. Thus, at step 527, the leakdetection processor 473 compares the amplitude V_(f,A) of the firstvoltage signal 253A to the amplitude V_(f,B) of the second voltagesignal 253B. If the leak detection processor 473 determines that theamplitude V_(f,A) of the first voltage signal 253A is significantlydifferent than the amplitude V_(f,B) of the second voltage signal 253B,it provides an indication of a detected leak at step 529. If the leakdetection processor 473 determines the amplitudes V_(f,A), V_(f,B) ofthe first and second voltage signals 253A, 253B are substantially equal,it returns to steps 511 and 513 at step 531. In one or more embodiments,the leak detection processor 473 compares the amplitude V_(f,A) of thefirst voltage signal 253A to the amplitude V_(f,B) of the second voltagesignal 253B by calculating a difference between the first and secondvoltage signals and comparing the calculated difference to a threshold(e.g., a constant threshold or a variable threshold determineddynamically, for example, as a percentage of either of the amplitudesV_(f,A), V_(f,B)). When the leak detection processor 473 determines thedifference between the amplitudes V_(f,A), V_(f,B) of the first andsecond voltage signals 253A, 253B exceed the threshold, it provides anoutput indicative of a detected leak.

The leak detection systems 241, 441 and the methods 301, 501 fordetecting a leak in a flowmeter 201 advantageously eliminate the effectsof the DC potential between the first and second electrodes 215A, 215Band other sources of noise by using Fourier analysis to isolate thecontent of the voltage signals 253A, 253B at the drive frequency f fromportions of the signal. The amplitude(s) of the voltage signals 253A,253B at the drive frequency f represent the flow-induced portion of thevoltage signals and suppress other portions of the voltage signals.Thus, only those portions of the voltage signals 253A, 253B thataccurately reflect whether the voltage signals properly vary withperiodic changes in the electromagnetic field are used to determinewhether a leak affects either of the voltage signals. It is believedthat isolating the flow-induced portions of the voltage-signals 253A,253B from other portions of the signals inhibits noise, such as DCpotentials inherent in the voltage signals, from significantlyinfluencing the leak determination results. In addition, theconstruction of the insulating sleeves 117, 217 creates a direct fluidpath between the electrodes 115, 215A, 215B and the respective flowtubewalls 105, 205, which creates an intentional short circuit when a leakis present that is readily detectable using the leak detection systems141, 241, 441.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements. In view of the above, it will be seen that the several objectsof the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions, products,and methods without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:
 1. A leak detection system for detecting a leak inan electromagnetic flowmeter having an electromagnetic field source forgenerating an electromagnetic field in a fluid flowing through theflowmeter that changes periodically at a drive frequency and first andsecond electrodes to detect a voltage induced in the fluid, said leakdetection system comprising: a leak detection processor connected to thefirst and second electrodes to receive first and second signalsrepresentative of the voltage detected by the first and secondelectrodes, respectively, the leak detection processor being configuredto analyze a content of at least the first signal at the drive frequencyto determine whether the first signal is affected by a leak in theflowmeter and provide an output indicative of a detected leak when theleak detection processor determines that the first signal is affected bythe leak in the flowmeter.
 2. The leak detection system of claim 1further comprising a summing amplifier connected to the first and secondelectrodes to receive the first and second signals, the summingamplifier being configured to add the first and second signals togenerate a summation signal received by the leak detection processor. 3.The leak detection system of claim 2 wherein analyzing the content ofthe first signal at the drive frequency comprises analyzing a content ofthe summation signal at the drive frequency to determine whether eitherof the first signal and the second signal is affected by a leak in theflowmeter.
 4. The leak detection system of claim 3 wherein the leakdetection processor is configured to compare said content of thesummation signal at the drive frequency to a threshold to determinewhether either of the first signal and the second signal is affected bya leak in the flowmeter.
 5. The leak detection system of claim 4 whereinthe leak detection processor is configured to receive a differencesignal representative of a magnitude of a difference between the firstsignal and the second signal and to dynamically determine the thresholdas a percentage of the difference signal.
 6. The leak detection systemof claim 5 wherein said percentage is from about 10 percent to about 40percent of the difference signal.
 7. The leak detection system of claim3 wherein the leak system is configured to sample the summation signalduring a sampling interval to create a sample set corresponding in timewith one or more complete drive cycles.
 8. The leak detection system ofclaim 7 wherein said content of the summation signal at the drivefrequency is an amplitude of the summation signal at the drive frequencyand wherein the leak detection processor is configured to determine saidamplitude from the sample set using Fourier analysis.
 9. The leakdetection system of claim 2 further comprising a high pass filterconnected between the summing amplifier and the leak detection processorto suppress a portion of the summation signal attributable to a DCpotential between the first and second electrodes.
 10. The leakdetection system of claim 1 wherein the leak detection processor isfurther configured to analyze a content of the second signal at thedrive frequency to determine whether either of the first signal and thesecond signal is affected by a leak in the flowmeter.
 11. The leakdetection system of claim 10 further comprising a multiplexeroperatively connected to the first and second electrodes to receive thefirst and second signals, the multiplexer being configured to generate amultiplexed signal comprising an alternating sequence of the first andsecond signals, the leak detection processor receiving the first andsecond signals from the multiplexed signal.
 12. The leak detectionsystem of claim 10 wherein the leak detection processor is configured tocompare said content of the first signal with said content of the secondsignal to determine whether either of the first signal and the secondsignal is affected by a leak in the flowmeter.
 13. The leak detectionsystem of claim 12 wherein the leak detection system is configured tosample the first signal during a first sampling interval to create asample set of the first signal corresponding in time with one or morecomplete drive cycles and to sample the second signal during a secondsampling interval to create a sample set of the second signalcorresponding in time with one or more complete drive cycles.
 14. Theleak detection system of claim 13 wherein said content of the firstsignal is an amplitude of the first signal at the drive frequency duringthe respective one or more complete drive cycles and said content of thesecond signal is an amplitude of the second signal at the drivefrequency during the respective one or more complete drive cycles, theleak detection processor determining the amplitudes of the first andsecond signals from the sample set of the first signal and the sampleset of the second signal using Fourier analysis.
 15. The leak detectionsystem of claim 14 wherein the leak detection processor is configured todetermine whether a difference between the determined amplitudes of thefirst and second signals exceeds a threshold.
 16. The leak detectionsystem of claim 1 in combination with said electromagnetic flowmeter,said electromagnetic flowmeter comprising; a flowtube configured tocarry the fluid, the flowtube having a flowtube wall comprising aconductive material, the flowtube wall having an inner surfacesurrounding a fluid flow path for the fluid; a non-conductive linerpositioned to electrically insulate the flowtube wall from the fluid,the flowtube and non-conductive liner defining first and secondelectrode mounting holes; the first and second electrodes extendingthrough the first and second electrode mounting holes, respectively, thefirst and second electrodes and the non-conductive liner formingrespective fluidic seals between the first and second electrode mountingholes and the fluid flow path, at least a portion of each of the firstand second electrodes being arranged in fluid communication with theflowtube within the respective electrode mounting hole.
 17. A method fordetecting a leak in an electromagnetic flowmeter having anelectromagnetic field source configured to generate an electromagneticfield in a fluid flowing through the flowmeter that changes periodicallyat a drive frequency and at least first and second electrodes configuredto detect a voltage induced in the fluid in response to theelectromagnetic field, said method comprising: analyzing a content of asignal from at least one of the first and second electrodes at the drivefrequency; detecting a leak in the flowmeter using said content of thefirst signal; and providing an indication of a detected leak when theleak is detected.
 18. The method of claim 17 wherein analyzing a contentof a signal comprises summing a first signal from the first electrodeand a second signal from the second electrode to generate a summationsignal and analyzing a content of the summation signal at the drivefrequency to determine whether either of the first signal and the secondsignal is affected by a leak in the flowmeter.
 19. The method of claim18 wherein analyzing a content of the summation signal comprisescomparing said content of the summation signal at the drive frequency toa threshold to determine whether either of the first signal and thesecond signal is affected by a leak in the flowmeter.
 20. The method ofclaim 19 further comprising generating a difference signalrepresentative of a magnitude of a difference between the first signaland the second signal and dynamically determining the threshold as apercentage of the difference signal.